Calculation of Density of a Crystal:
If we know the edge length of a cubic crystal of an element or a compound, density can be easily calculated.
Consider a unit cell of edge ‘a’ picometer (pm),
Then, the length of the edge of the cell = a pm.
= a x 10-12 m
= a x 10-10 cm
Volume of the unit cell = (a x 10-10cm) 3 = a3 x 10-30 cm
Density of the unit cell =Mass of unit cell/Volume of unit cell
Mass of unit cell = No. of atoms in a unit cell x Mass of each atoms
= Z x m
Where, Z = Number of atoms in unit cell
= Z x M/ N0 m = Mass of each atom = M/N0
Density of the unit cell =Z x M/ (a3 x 10-30 x N0